Nuclear fuel rod loading method and apparatus

ABSTRACT

A method to load a nuclear fuel rod, comprising, providing nuclear fuel pellets in a bottomless tray; transferring the nuclear fuel pellets from the bottomless tray to a fuel pellet column through the use of a belt, indexing the nuclear fuel pellets in the fuel pellet column to a nuclear fuel pellet loading machine; and pushing the fuel pellet column into a fuel rod cladding.

FIELD OF THE INVENTION

The present invention relates to nuclear fuel assemblies. Morespecifically, the present invention provides a method and device to loada nuclear fuel rod for a nuclear fuel assembly.

BACKGROUND INFORMATION

Production for nuclear fuel assemblies requires significant care duringfabrication. The fabrication steps taken for such fuel assemblies isoften costly and complicated due to the amount of precautionary stepsthat are required. Nuclear fuel rods are designed with several differentcomponents, wherein each of the components having a specific designpurpose. The fissionable component of each nuclear fuel rod is generallya uranium enriched ceramic material (a uranium oxide) that is shaped inthe form of a pellet. Individual pellets are placed end to end to form afuel column. The fuel column is then inserted into an elongated rod madeof corrosion resistant metal, such as a zirconium alloy, called a fuelclad. The fuel column is protected from mechanical and chemical wear bythe fuel clad. The fuel clad protects the fuel column during operationof the reactor as well as handling of the fuel assembly. As anadditional precaution, springs and/or other devices are also includedinside the volume encapsulated by the fuel clad to allow the uraniumfuel elements to swell and shift within prescribed limits in the fuelclad. This allows the fuel column to withstand several different loadingscenarios without detrimental effects to the fuel column. The completedfuel rods are then stored. Completed fuel rods are then placed in aparallel arrangement, called a fuel assembly, to prevent the fuel rodsfrom contacting each other during use.

Currently used devices and methods to incorporate the nuclear fuelelements into the fuel clad have several drawbacks and are therefore noteconomically efficient. The production of nuclear fuel rods requiresquality assurance checks to ensure that defects do not occur during theproduction of the nuclear fuel rods. To eliminate human error, manytechnologies attempt to use automated systems to eliminate workerinvolvement in the process. Although well intentioned, the automatedsystems must be carefully designed such that during fabrication of thefuel rod, no loose pieces and/or parts are generated which will jam themachine and stop production. The creation of these automated systems isextremely complicated and the systems created are prone to error due tothe inability of designers to accurately predict the failure modes andproblems encountered during production of the fuel rods.

In current automated loading systems, nuclear fuel pellets are takenfrom a fuel pellet elevator and transferred by a conveyor in a tray to asegment make-up table. The fuel pellets are removed from the fuel pellettray by a worker and placed on the table. The fuel pellets are placed ina parallel orientation and then compacted by a pusher device to formcolumns of uranium containing ceramic material. The pushing device isconnected to a linear variable displacement transducer which isconfigured to provide an electrical output signal. The electrical outputsignal is then read by a computer and an overall length of theindividual fuel element column is determined. A computer then comparesan overall design specification for the fuel rod with the overall lengthdetermined from the output signal. If the difference between theexpected design value of the nuclear fuel element column length and themeasured value meets a predetermined threshold value, the fuel rodcladding is then loaded with the nuclear pellet column. If the overalllength of the fuel pellet column is outside of the threshold value, thefuel pellets are then rejected from the segment make-up table. A top endcap is then welded the existing open side of the fuel rod claddingthereby completing the nuclear fuel rod.

There is a need to provide an apparatus and method which will enable anoperator to perform additional quality assurance checks of the nuclearfuel elements during the manufacturing process of a nuclear fuel rod.

There is also a need to provide a method and device to load nuclear fuelpellets into a nuclear fuel rod in a safe, economical and non-damagingmanner.

There is a further need to provide a method and device which will loadcylindrical fuel pellets into an open fuel rod clad, i.e. a fuel rodclad without a lower plug welded to the fuel clad.

There is a further need to provide a method and device which will allowcylindrical fuel pellets to be loaded into an open fuel rod clad toeliminate slow insertion speeds for pellet placement found in existingmethods and systems.

SUMMARY

It is therefore an objective of the present invention to provide amethod and device to load pellets into a nuclear fuel rod for a nuclearfuel assembly.

It is also an objective of the present invention to provide a method anddevice to load nuclear fuel pellets into a nuclear fuel rod in a safe,economical and non-damaging manner.

It is also an objective of the present invention to provide a method anddevice which will load cylindrical fuel pellets into an open fuel rodclad.

It is a further objective of the present invention to provide a methodand device which will allow cylindrical fuel pellets to be loaded intoan open fuel rod clad to eliminate slow insertion speeds for pelletplacement found in existing methods and systems.

The objectives of the present invention are achieved as illustrated anddescribed. The present invention provides a method to load a nuclearfuel rod, comprising the steps of providing nuclear fuel pellets in abottomless tray, transferring the nuclear fuel pellets from thebottomless tray to a fuel pellet column through the use of a belt;indexing the nuclear fuel pellets in the fuel pellet column to a nuclearfuel pellet loading machine, and pushing the fuel pellet column into afuel rod cladding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a bottom tray supporting fuel elements to beincorporated into a nuclear fuel rod.

FIG. 2 is top perspective view of a pushing blade system for offloadingnuclear fuel elements into the bottomless tray.

FIG. 3 is a top view of a bottomless tray and associated drive unit.

FIG. 4 is a side view of the bottomless tray and associated drive unit.

FIG. 5 is a side perspective view of a transfer belt for unloading abottomless tray.

FIG. 6 is a top view of a juxtaposition of a transfer belt and a fuelplate transfer unit for use in transferring fuel elements to a loadingarea.

FIG. 7 is a top view of a rod loading device.

DETAILED DESCRIPTION

Referring to FIG. 1, a bottomless tray 10 is illustrated. The bottomlesstray 10 provides a housing by which nuclear fuel elements, in theillustrated embodiment fuel pellets 12, are transported for ultimateincorporation into open end nuclear fuel clad. The tray 10 houses thenuclear fuel pellets 12 such that the tray 12 traverses along a pathwaywhich supports the pellets 12. The bottomless tray 10 is made of ahardened corrosion resistant material, such as stainless steelcompatible with nuclear materials.

Referring to FIG. 2, a handling tray 10 enters an unloading area 38where nuclear fuel pellets 12 are to be inserted into the bottomlesstray. A hydraulic actuator 22 provides a motive force which causessupports 20 to extend in direction 24. The hydraulic actuator 22 isactivated through the instruction of a computer 25, which has sensors 27that indicate the presence of a handling tray 10. At a first end of thesupports 20, a pushing blade 18 is positioned at a height which contactsthe fuel pellets 12 in the handling tray 10 along the individual rows40. The blade 18, in the example embodiment illustrated, is a flatbottom device. In an alternate embodiment of the present invention, theblade 18 has a scalloped edge. The blade 18 and the associated supports20 move in direction 24 to push the fuel pellets 12 off of the tray 10.At the completion of the pushing of the fuel pellets 12 off of the tray10, the blade 18 is then lowered by the hydraulic actuator 22 such thatthe edge contacts the tray 10. The actuator 22 may be any unit thatprovides movement of the supports 20 and the associated blade 18. Assuch, the actuator 22 may be an electromechanical device, a geareddevice or other similar arrangement. The actuator 22 may also beconfigured with a failsafe design to limit the imposition of force uponthe fuel elements during pushing. To this end, the actuator 22 may beconfigured with a trip circuit that disconnects actuation of the powerto the actuator if force is measured by the actuator to be above apredefined amount. The blade 18 is then moved in a tray removaldirection 26. The impact of the blade 18 on the tray 10 removes the tray10 from the conveyor belt 29. The tray 10 may then be stacked forfurther usage at another time. The conveyor belt 29 may then be indexedby the computer 25 to provide another handling tray 10 into the loadingarea The process of unloading fuel elements may then be repeated asoften as desired. In the illustrated embodiment provided, a handlingtray may be loaded every approximately 15 seconds.

A new tray 10 may then be moved into place along the roller system suchthat the pushing blade 18 is in a renewed position to push additionalfuel pellets from the bottomless tray.

FIG. 3 is a top view of a fuel plate transfer unit 30. The bottomlesstray unit 30 accepts fuel pellets 12 pushed by the combination of thehydraulic actuator 22 and the pushing blade 18. The fuel plate transferunit 30 has fuel element rows 28 which correspond to the fuel elementsplaced upon the handling tray 10. Once the individual fuel elements areloaded into the bottomless tray rows 28, the individual fuel elementsare then removed from the element rows 28 through indexing of the fuelplate transfer unit 30. The indexing of the fuel elements from thebottom of the fuel plate transfer unit 30 occurs along the indexingdirection 32. The indexing occurs through the use of a motor 36 inconjunction with a rail 34. A slot 41 placed below the fuel platetransfer unit 30 allows the individual fuel elements rows to fall fromthe side of the bottomless tray unit 30 into the slot 41. The pelletsare then transferred down the slot 41 through the use of a belt 42. Thenumber of rows in the fuel plate transfer unit 30 and the bottomlesstray 10 may be augmented such that larger or smaller batches of fuelelements 12 may be processed through the pellet loading apparatus. Thefuel plate transfer unit 30 is indexed along direction 32 by the motor36 through a ball screw connection. The ball screw is driven throughmotors controlled by a computer 37. Although illustrated as a chaindriven motor arrangement, other methods of operation such as hydraulicmovement of the fuel plate transfer unit 30 are possible. The length ofthe rail 34 is such that the fuel plate transfer unit 30 can index allrows of fuel pellets into the single slot 41.

Referring to FIG. 4, a side elevational view of the fuel plate transferunit 30 is illustrated. The fuel plate transfer unit 30 indexes alongdirection 32 such that individual fuel elements 46 fall from theunderside of the bottomless tray unit 30. The rotational belt 42 acceptsfuel pellets 46 falling from the fuel plate transfer unit from the slot41. A fuel pellet block 48 protects the alternate side of the slot 41such that the individual fuel elements 46 directly drop into the slot 41and onto the rotational belt 42. The individual fuel elements 46 arehoused in openings 31 placed in the bottomless tray 30. The openings 31are sized to allow the fuel elements 46 to roll along an interfacingsurface 33, but also keep individual fuel pellets from interacting withother fuel pellets during the indexing. Both the surface of the openings31 and the interfacing surface 33 are configured as smooth surfaces tolimit damage to the fuel elements 46. The width of the slot 41 isminimized to restrict the amount of movement of the fuel element 46along the indexing direction 32. The depth of the slot 41 is also chosensuch that fuel elements which transfer to the belt surface do notinterfere with the indexing of the fuel plate transfer unit 30 duringfurther indexing operations. Additionally, the speed of the rotationalbelt is maintained at levels that do not cause the fuel element 46 whichtransfers to the belt surface to jump do to sudden impartation of force.Although illustrated as a rectangular slot configuration, the slot 41may also have an hourglass design to limit the possibility of fuelelements from being ejected from the surface of the belt 42 and back tothe fuel plate transfer unit 30. The illustrated embodiment is intendedfor use on a level floor. If the pellet loading apparatus is to be usedon a non-level surface, the belt 42 can be provided with protection forfuel element slide back by increasing the coefficient of frictionbetween the fuel element and the belt. An example of this is placing arubber coating on the belt 42. The belt 42 can be configured to assessmaterial weight placed on the belt 42. Additionally, the belt 42 mayhave a belt speed sensor and a microprocessor-based integrator tocontinuously compute the rate of materials transferred along the entirelength of the conveyor per unit time. The belt 42 surface can bemaintained in a taught configuration through a screw take-up system 51which maintains a desired spacing between the individual rollers 52.Although the loads handled by the belt 42 are anticipated to be light,impact idlers may be added in the impact area of the slot 41 to minimizebelt deflection during loading. To additionally keep the belt surfacetaught, carrying idlers 53 can be accommodated along the entire spacebetween the rollers 52. A take up weight 55 is also located along thebelt 42 to keep the top surface of the belt 42 in a taught conditionunder increasing and decreasing speeds as well as changes in temperatureand humidity.

Referring to FIG. 5, the rotational belt 42 is illustrated in moredetail. The rotational belt 42 is an endless loop of material 50 whichis driven by motor driven rollers 52. The motor driven rollers 52 arecontrolled through a controller, such as a computer. The speed of themotor driven rollers 52 and the rotational belt 42 may be a constantspeed or may be variable according to the needs of the process. Theendless loop of material 50 is provided to safely transfer ceramic tilefuel elements along the length of the rotational belt 42 without damage.In the example embodiment illustrated, the rotational belt may be a PVCmatrix belt, a rubber track belt, or other arrangement which provides anon-maring surface to contact the individual fuel elements.

Referring to FIGS. 6 and 7, individual fuel elements are stacked to makeup the full fuel rod pellet column by the rotational belt 42 are thenloaded into a fuel element transfer apparatus 70. The fuel elementtransfer apparatus 70 accepts the individual fuel elements in a lineprogression to form a fuel column. The fuel column is then transportedfrom the fuel element transfer apparatus 70 into an open ended fuel clad72 placed in the fuel element transfer apparatus 70. A blade 74 operatedby a motor 76 pushes the fuel column down the fuel element transferapparatus 70 and into the fuel clad 72. The blade 74 and the motor 76are controlled by a computer 80 which has positional sensors 77indicating the amount of fuel elements within the fuel element transferapparatus 70. Instructed by the computer 80, the motor 76 is activatedand the blade 74 transfers the fuel column into the open ended fuel clad72. The fuel element transfer apparatus 70 is constructed such that thefuel column can be pushed into the fuel clad 72 without damage or needfor lifting of the fuel elements. The blade 74 travels along guides 82thereby allowing the blade 74 to maintain a perpendicular orientation tothe fuel column placed within the fuel element transfer apparatus 70.

The method and apparatus of the present invention provide significantadvantages over conventional methods and apparatus to load nuclear fuelpellets into fuel rod cladding. The present method and apparatus of thepresent invention allow an individual fuel rod to be loaded with nuclearfuel material with a typical cycle time of 30 seconds. Conventionalcycle times for pellet loaders have a typical cycle time ofapproximately 45 seconds.

The method and apparatus of the present invention provide for loading ofnuclear fuel rods such the elements making up the fuel column are notdamaged by hard loading. Furthermore, the present invention reducesradiation exposure for workers constructing nuclear fuel rods due to theincreased loading speed. Airborne contamination is reduced since openrod loading eliminates pressure buildup as the pellet column is inserted(gas escape over fuel column.)

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings areaccordingly to be regarded in an illustrative rather than in arestrictive sense.

1. A method to load a nuclear fuel rod, comprising: providing nuclearfuel pellets in a bottomless tray; transferring the nuclear fuel pelletsfrom the bottomless tray to a fuel pellet column through the use of abelt; indexing the nuclear fuel pellets in the fuel pellet column to anuclear fuel pellet loading machine; and pushing the fuel pellet columninto a fuel rod cladding.
 2. The method to load a nuclear fuel rodaccording to claim 1, wherein the pushing of the fuel pellet column isinto a fuel rod cladding open on both ends.
 3. The method to load anuclear fuel rod according to claim 1, wherein the step of transferringthe nuclear fuel pellets from the bottomless tray is through pushing allof the rows of nuclear fuel pellets into a fuel pellet row acceptancedevice.
 4. The method to load a nuclear fuel rod according to claim 1,wherein the pellets are provided in the bottomless tray on a supportingplate assembly.
 5. The method to load a nuclear fuel rod according toclaim 1, wherein the step of transferring the nuclear fuel pellets fromthe bottomless tray is through indexing the tray over the belt such thatindividual columns of fuel pellets are removed from the tray.
 6. Themethod to load a nuclear fuel rod according to claim 1, wherein the stepof indexing the nuclear fuel pellets in the fuel pellet column to anuclear fuel pellet loading machine is performed through a v-troughstation.
 7. The method to load a nuclear fuel rod according to claim 1,further comprising: verifying a length of the fuel pellet column afterthe step of indexing the nuclear fuel pellets in the fuel pellet columnto a nuclear fuel pellet loading machine.
 8. The method to load anuclear fuel rod according to claim 1, further comprising: welding alower end on the cladding.
 9. The method to load a nuclear fuel rodaccording to claim 8, further comprising: welding a top end on a top ofthe cladding.
 10. An apparatus to load a nuclear fuel rod clad,comprising: a bottomless tray arrangement; a pushing arrangement whichtranslates from a unloaded position to a second pushing position; a fuelplate transfer unit arrangement parallel to the bottomless trayarrangement, wherein fuel elements pushed by the pushing arrangement areplaced within the fuel plate transfer unit; a conveyor belt; an indexingsystem connected to the fuel plate transfer unit, the indexing systemmoving the fuel plate transfer unit over the conveyor belt; and a fuelelement transfer apparatus having a pushing apparatus and a fuel columnloading area, the fuel element transfer apparatus configured to receivethe fuel elements from the conveyor belt, and form a fuel column andfurther configured to push the fuel elements into a double ended openfuel clad.